Load center interior attachment

ABSTRACT

An electric load center having a basepan having a surface, the surface having a tab with a tapered lower edge and a prong extending from a side edge of the tab for capture by lances found in the enclosure of the load center.

FIELD OF THE INVENTION

The present invention relates generally to electric load centers, andmore particularly to an improved load center and load center components.

BACKGROUND OF THE INVENTION

Electric load centers suffer from a number of limitations. Assemblingthe various components of the load center such as the trim panel to themetal enclosure of the load center oftentimes requires an electrician toalign the holes in these components, insert screws through the alignedholes, and screw each screw into the holes. Such activities are timeconsuming and are oftentimes not successful on the first attempt andhave to be repeated several times. In accordance with an aspect of thepresent invention, a push-in screw holder fixture for the metalenclosure is provided which enables an electrician to easily secure thetrim to the metal enclosure.

There is sometimes created an overpressure condition within a loadcenter which can cause the door of prior art load centers to be forcedopen. In accordance with an aspect of the present invention, a new andimproved latch is provided which, during an overpressure conditionwithin the load center, causes the latch to engage the latch receptacleon the trim panel even more securely so that the door does not open.

Because load centers are constructed in varying sizes, for each size ofload center constructed by a manufacturer, a separate inventory ofbasepans had to be manufactured and maintained. A need has thereforedeveloped for basepans which are adaptable to various sized load centersand which are relatively inexpensive to manufacture. This need waspartially met by the production and use of extruded basepans.Alternatively, individual modular auxiliary basepan pieces wereconstructed for interconnection to accomplish circuit breaker loadcenters of adjustable length. Because angular mounting of components isnot well suited to robotic assembly, some prior art basepans and modularextensions have had to be adapted to be vertically down loaded to matingportions of the basepan, or have been adapted to be horizontally orlaterally connected to mating portions of the basepan. Such attachmentmethods and modular construction may not be desireable and can result inimprecise spacing between the connected modular pieces, which may affectthe subsequent assembly and installation of components to the basepanand the basepan to the enclosure. In accordance with an aspect of thepresent invention, new and improved basepan and modular extensionbasepan components are provided which can be robotically assembled, butneed not be robotically assembled in solely a vertical drop-down mode ora lateral mode, and which reduce the possibility of misalignment andimproper spacing between connected modular pieces.

Securing the basepan to the enclosure is oftentimes time consuming andcumbersome. In accordance with an aspect of the present invention, animproved basepan is provided having mounting features which facilitatethe assembly of the basepan to the enclosure, thus saving time andlabor.

It is well known in the art to provide an electrically insulativebarrier between the bus bars of load centers. In accordance with anaspect of the present invention, an improved basepan having integrallyformed electrical insulative barrier is provided between the bus barswhich increases the protection from the occurrence of arc tracking aswell as decreasing the possibility of sustaining the arc, once it hasoccurred.

Bus bars have been secured to the basepan by common fastening devicessuch as screws, bolts and snap-in fasteners (U.S. Pat. No. 4,536,823)which can be cumbersome, time consuming to apply, uneconomical, requireextra parts, and most importantly can impart stresses to the componentbeing secured and adversely effect the structural integrity of thecomponent. Applying ultrasonic energy to posts which are integral partsof a plastic basepan as a means of deforming the post to secure bus barsto the plastic basepan is well known (U.S. Pat. No. 4,118,754). Heatstaking as a means of securing components to a plastic basepan can beadvantageous in overcoming the above-stated disadvantages of commonfastening devices, but imparts stresses which concentrate at the face ofthe basepan where the base of the post intersects the basepan to formcorners. Such stress can significantly impair the integrity of theconnection by causing a fracture of the post, loss of the integrity ofthe connection, and a decrease in the service life of the basepan andthe load center. In accordance with an aspect of the present invention,an improved basepan is provided having integrally formed posts forsecuring thereto components such as bus bars and the like by heatstaking which reduces the stresses imparted to the posts and basepansfrom heat staking.

As is well known, it has been difficult for installers to secure returnwires to the neutral bars of the prior art load centers because it isgenerally difficult to see the holes in the neutral bar into which thewires are to be placed. In order to improve the visibility of the holesin the neutral bar into which the return wires of the power circuits areto be inserted and secured, and thereby facilitate the connection of theneutral return wires to the neutral bars by the electrical installer, inaccordance with an aspect of the present invention an improved neutralbar is provided which allows for viewing of the electrical connectorapertures positioned in the side walls when viewed either directlyoverhead or from the side.

Also, prior art attachment methods between the neutral bar and thebasepan are unsatisfactory. In accordance with an aspect of the presentinvention, the neutral bar is adapted to permit simplified assembly andmounting to the basepan. This is accomplished by providing aconfiguration of the neutral bar and an improved basepan to which theneutral bar is attached which does not require the use of screws orother separate fastening devices thereby reducing the number ofcomponents in the load center and facilitating the mounting of theneutral bar to the basepan.

Furthermore, in order to further facilitate the installation of thereturn wires to the neutral bars of the load center, in accordance withan aspect of the present invention, an improved basepan is providedhaving an integrally formed neutral bar wire guide which assists theelectrician or installer in guiding the wires of power distributioncircuits into the electrical connector apertures in the neutral bars.

In accordance with another aspect of the present invention, an improvedneutral tie bar is provided which connects the neutral bars together.Some load centers of the prior art are not grounded because theinstaller or user neglects to do so. There is nonetheless a need toassure that there is no potential difference between the neutral and theground. In accordance with this aspect of the present invention, theneutral tie bar is adapted to be capable of being electrically connectedto the outer metal enclosure of the load center thereby eliminating anypotential difference between the neutral and ground of the load center.Since each power company providing service maintains the potential ofthe neutral at or close to zero volts, the function of connecting theneutral of the load center to the ground is accomplished by electricallyconnecting the neutral tie bar to the metal outer enclosure.

In accordance with an aspect of the present invention, a new andimproved main lug insulator or barrier is provided between the incomingservice and the other components in the load center functions to:insulate each of the main lugs from the neutral bus bar, neutral tiebar, and neutral lug(s); reduce incidental shorting or inadvertentenergization of current carrying conductors both during installation andsubsequent operation; and maintain required over-surface and through-airspacing for cooling and expansion of the main lugs.

SUMMARY OF THE INVENTION

In accordance with the invention, the enclosure of the load center isadapted to receive and is fitted with a push-in screw holder fixturecomprising an open ended u-shaped structure formed by folding a piece ofsheet metal having; (a) an upper surface having two tabs formed therein,facing one another and directed inward and downward, each of said tabshaving a free edge forming an opening therebetween for receiving thethreads of a screw and which deflect upon axial pressure to form a oneway opening, the upper surface further having two outwardly extendingflanges; and (b) two sidewalls extending downward and substantiallyorthogonal from the upper surface, each of said sidewalls having a tabformed therein and directed outwardly and upwardly for clasping an edgeof the hole between the upwardly and outwardly directed tab and theoutwardly extending flange.

The door latch of the load center comprises a one-piece molded memberdisposed in an opening in the door, the one-piece member having a planartop with an indent for opening the latch, a body portion extending froman underside of the planar top which is slideably received in an openingin the door, the body portion having a flexible tongue extending in anupwardly direction at an angle away from the body and towards the freeedge of the door. The one-piece molded member further includes a hookdisposed from the underside of the top, the hook having a free endextending toward the tongue of the body for engaging an underside edgeof a portion of a trim panel of the load center and which is adapted toform an aperture adjacent the opening in the door. The tongue urges thedoor latch towards the first edge of the door, keeping the hook biasedlyengaged with the underside edge of the portion of the trim panel adaptedto form the aperture.

The basepan of the load center is an integrally formed snap-on basepancomprising a one piece molded member having a planar surface formounting the bus bars, at least one circuit breaker support railextending upward from said planar surface for supporting the circuitbreakers in the load center, the circuit breaker support rail having atone end an upper end wall and at a second end a lower end wall, saidlower end wall being adapted to have a slot with an upper edge. Thesnap-on basepan having at least one modular extension mounting footextending from the lower end wall for receiving a modular extensionbasepan to extend the length of the snap-on basepan. The modularextension mounting foot comprising an upper wall and two sidewalls and afront wall and a rear wall being arranged to form a hollow rectangularbox, said rear wall being formed by the end wall of said circuit breakersupport rail, the upper wall and one of the two sidewalls of the modularextension mounting foot having a trapezoidal shaped slot extendingtherethrough for engagement by a correspondingly shaped ramp of themodular extension basepan to align the modular extension basepan to thesnap-on basepan. The upper wall of the modular extension mounting footfurther including an aperture for passing therethrough a flexible snaphook extending from the modular extension basepan to engage the upperedge of the slot formed in the lower end wall of the circuit breakersupport rail and to thereby secure the modular extension basepan to thesnap-on basepan.

The basepan of the load center comprises a planar surface for themounting of bus bars, the planar surface having a tab extending from anedge of the planar surface, the tab having a tapered lower edge and aprong extending from a side edge. The basepan further having earsextending from the planar surface and disposed toward opposite sides ofthe basepan, each of the ears having an aperture for the passage of ascrew. The enclosure of the load center has a lance formed from abackwall, the lance having a free end disposed away from the backwalland into the interior of the enclosure for capturing the tab of thebasepan, the enclosure further having a hole in the backwall forreceiving a screw. As the basepan is being mounted to the enclosure, thetapered lower edge of the tab is captured between the lance formed inthe backwall of the enclosure and the interior face of the backwall andthe prong is engaged by an upper edge of the tab to stop the verticalmovement of the basepan while the ears of the basepan are placed intoabutting relation with the interior surface of the backwall for mountingby a screw through the aperture and into the correspondingly positionedhole in the enclosure.

The basepan of the load center comprises a planar surface for receivingfirst and second bus bars, the planar surface having two spaced apartsubstantially parallel walled members integrally formed with andextending substantially orthogonally upwards from the planar surface toform a continuous double-walled barrier between the first bus bar andthe second bus bar.

The basepan of the load center comprises a surface to which a selectedcomponent of the load center is to be mounted, the surface having atleast one integrally formed post for peening over by heat staking tosecure the selected component to the basepan, wherein the integrallyformed post has a torroidal shaped undercut extending around a peripheryof the post at the intersection with the surface of the basepan.

In accordance with an aspect of the present invention, a neutral bar isprovided having an elongated central body portion with a trapezoidalshaped cross-sectional area with outwardly sloping downwardly extendingside walls, the side walls having a plurality of apertures for insertionof electrical wires, a top portion extending from the central bodyportion and having a plurality of tapped holes at least one of which isin communication with a corresponding one of the plurality of aperturesin the side walls, and a base portion extending from the central bodyportion for mounting to the basepan.

The basepan of the load center comprises a surface member for mountingcomponents of the load center and a channel for mounting a neutral barhaving a plurality of electrical connector apertures for receivingneutral return wires, the surface member further including an integrallyformed neural bar wire guide comprising a wall upwardly extending fromthe surface member, the wall having semicircular slots extendingtherethrough at an upper surface, each one of the semicircular slots forreceiving a return wire and guiding the return wire therethrough andinto a preselected one of the plurality of electrical connectorapertures in the neutral bar.

An improved neutral tie bar for connecting together the neutral bars ofa load center having a metal outer enclosure, the neutral tie barcomprising: (a) a center portion having two vertically offset laterallyextending ends, each of said ends having an aperture for receiving ascrew to secure each of said ends to a neutral bar; (b) a pair of firstelevated members, each one of said pair of first elevated members beingdisposed between the center portion and one of said ends and adapted toform a branch neutral cable lug having a horizontally disposed bore forreceiving a branch neutral cable, the branch neutral cable lug furtherhaving a vertically extending tapped bore in communication with thehorizontally disposed bore, said vertically extending tapped bore forreceiving a threaded clamping screw to secure the branch neutral cable;(c) a second elevated member disposed between one of said pair of firstelevational portions and one of the vertically offset laterallyextending ends, said second elevated member being adapted to form aneutral cable lug having a horizontally disposed bore for receiving aneutral cable, the neutral cable lug further having a verticallyextending tapped bore in communication with the horizontally disposedbore, said vertically extending tapped bore for receiving a threadedclamping screw to secure the neutral cable. The neutral tie bar can beelectrically connected to the metal outer enclosure of the load center.

A main lug insulator for an electric load center, comprising: a firstand a second trough-shaped longitudinally extending compartment, each ofsaid first and second compartments comprising a horizontally disposedplatform from which extends two upstanding walls having first edgeswhich form a first open end and having second edges which form anoppositely facing second open end; a first support leg extendingdownward from the first edges forming said first open ends; a secondsupport leg extending downward from the second edges forming said secondopen ends; said first support leg being spaced apart and substantiallyparallel to said second support leg to form an open laterally extendingspace therebetween and below the platforms for positioning over aneutral tie bar of the load center.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the load center incorporating theprinciples of the present invention;

FIG. 2 is a plan view of the outer enclosure of the load center shown inFIG. 1;

FIG. 3 is a plan view of the trim panel which encloses the outerenclosure shown in FIG. 2;

FIGS. 4A, 4B, and 4C are top and side views of a push-in screw holder;

FIG. 5 is a front view of the door mounted to the trim panel shown inFIG. 3;

FIGS. 6A and 6B are perspective views of the door latch from above andbelow respectively;

FIG. 6C is a side view of the door latch;

FIG. 6D is a sectional view of the door latch shown in FIG. 6A takenalong line 6d-6d;

FIG. 6E is a sectional view of the door latch mounted to the door andsecured closed to the door trim;

FIG. 7 is an isolated perspective view of the basepan shown in FIG. 1;

FIG. 8 is a top plan view of the basepan shown in FIG. 7;

FIG. 9 is an enlarged plan view of a modular extension mounting foot ofthe basepan shown in FIGS. 7 and 8;

FIG. 10 is a sectional view of the modular extension mounting foot takenalong line 10--10 in FIG. 9;

FIG. 11 is a sectional view of the modular extension mounting foot takenalong line 11--11 in FIG. 9;

FIG. 12 is a top plan view of a modular extension basepan for connectionto the basepan shown in FIGS. 7 and 8;

FIG. 13 is a sectional view of the modular extension basepan taken alongline 13--13 in FIG. 12;

FIG. 14 is a sectional view of a portion of the modular extensionbasepan taken along line 14--14 in FIG. 13;

FIG. 15 is an enlarged plan view of the mounting foot of the modularextension basepan shown in FIG. 12;

FIG. 16 is a sectional view of a portion of the mounting foot takenalong line 16--16 in FIG. 15;

FIG. 17 is a sectional view of a portion of the mounting foot takenalong line 17--17 in FIG. 15;

FIG. 18 is a sectional view of the basepan taken along line 18--18 inFIG. 8;

FIG. 19 is a sectional view of the enclosure taken along line 19--19 inFIG. 2;

FIG. 20 is a perspective view of the interior components of the loadcenter in FIG. 1 showing the basepan with circuit breakers removed;

FIG. 21 is an enlarged plan view looking down on a portion of thebasepan shown in FIG. 20 taken along line 21--21;

FIG. 22 is a sectional view taken along line 22--22 in FIG. 21 showing adouble walled serpentine barrier between the bus bars;

FIG. 23 is a sectional view taken along line 23--23 of the integrallyformed hollow post shown in FIG. 8;

FIG. 24 is a sectional view taken along line 24--24 of the integrallyformed solid post shown in FIG. 8;

FIG. 25 is a cross-sectional view of a neutral bar taken along line25--25 in FIG. 20;

FIG. 26 is a top view of the neutral bar shown in FIG. 20;

FIG. 27 is a cross-sectional view of upwardly extending flexible snaphook taken along line 27--27 in FIG. 8;

FIG. 28 is a side elevational view of neutral bar wire guide taken alongline 28--28 in FIG. 8;

FIG. 29 is a sectional view of the neutral tie bar taken along line29--29) in FIG. 30;

FIG. 30 is a top view of the neutral tie bar shown in FIG. 20;

FIG. 31A is a perspective view of the main lug insulator shown in FIGS.1 and 20;

FIG. 31B is a top view of the main lug insulator;

FIG. 31C is a sectional view of the main lug insulator taken along line31C--31C in FIG. 31B;

FIG. 31D is a rear elevational view of the main lug insulator shown inFIG. 31A; and

FIG. 31E is a side view of the main lug insulator shown in FIG. 31A.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, a load center for use in residential or lightcommercial applications is indicated in FIG. 1 by the referencenumeral 1. The load center 1 includes an enclosure 10, trim panel 50,supporting basepan 200 mounted therein, door 80, door latch 120, busbars 400 and 440, neutral bars 500, neutral tie bar 550, main lugs 420and 460, neutral lug 574, main lug insulator 600, and distributioncircuit breakers. Although not shown, load center 1 may alternativelyinclude a main circuit breaker instead of main lugs 420 and 460 whichconnect the incoming service or main lines to the components of the loadcenter and which functions to provide a means to interrupt power to theload center.

Referring to FIG. 2, enclosure 10 comprises a backwall 12 and fourintegral sidewalls 14,16,18 and 20 which terminate in inwardly turnedperipheral lips 22,24,26 and 28 respectively, surrounding an open frontof enclosure 10. Enclosure 10 is typically manufactured from sheet metalin a series of operations including cutting, blanking, forming andwelding. Enclosure 10 is typically installed between the wall studs of abuilding partition, so that the open side of the enclosure is flush withthe partition outer surface. Enclosure 10 is covered by a trim panel 50shown in FIG. 3 for flush fit with the enclosure and the partition. Trimpanel 50 is attached to enclosure 10 with fasteners, such as screws,which pass through holes 52 formed in the trim panel and into peripherallips 22 and 26 of sidewalls 14 and 18 shown in FIG. 2. The trim panel 50has a hinged access door secured by a latch which allows access to theinterior of the load center so as to permit user manipulation of circuitbreaker actuation handles located in the load center.

When installing a trim panel to an enclosure of the prior art, theelectrician generally has to align the holes formed in the trim panelwith the corresponding holes located in the enclosure, insert screwsthrough the aligned holes, and screw each screw into the enclosure. Thistask is time consuming and is oftentimes not successful on the firstattempt and has to be repeated several times.

In accordance with an aspect of the present invention, enclosure 10 isadapted to receive and is fitted with a push-in screw holder fixturewhich enables an electrician to secure trim panel 50 to enclosure 10 bymerely pushing a screw through the hole 52 in the trim panel and intothe push-in screw holder mounted in a lip of the enclosure.

Referring to FIGS. 4A, 4B and 4C, push-in screw holder 40 is shown andcomprises an open ended, "U"-shaped structure, formed of a single pieceof sheet metal where the U-shape is formed by folding the sheet metal toform an upper surface 41 and two sidewalls 43 extending from the uppersurface. The upper surface 41 has two outwardly directed flanges 42. Aone way opening 49 is formed in upper surface 41 by two tabs 44 directedinward and downward as more fully discussed below, to receive a threadedfastener. At each of two opposite sidewalls 43 is a cut out tab 46directed outwardly and upwardly. A push-in screw holder fixture 40 isinserted within correspondingly shaped holes 30 in lips 22 and 26 (shownin FIG. 2). Outward extending flanges 42 aid in fixing the push-in screwholder 40 in place in hole 30 in the enclosure, clasping the edges ofhole 30 between the outwardly extending flanges 42 and the upwardly andinwardly directed tabs 46.

At the time of installation of the trim panel 50 to enclosure 10, trimpanel holes 52 are aligned with push-in screw holders 40 in lips 22 and26 of enclosure 10, and a screw is pushed through each of the trim panelholes 52 and into the one-way opening 49 in each of the push-in screwholders 40.

Inward and downward cut out tabs 44 of push-in screw holder 40 act asspring-loaded fingers or leaf springs which deflect upon the axialpressure being exerted by a screw being pushed into the push-in screwholder. The free edges 47 of tabs 44 forming opening 49 engage thethreads of the screw thereby precluding linear withdrawal (i.e., pullingthe screw out in the opposite direction to the direction of insertion)without rotation of the screw in a counterclockwise direction.

In the event of an overpressure condition within a load center which canbe caused for example by a short circuit fault, the door of some priorart designed load centers can be caused to burst open. Morespecifically, the door can be bowed outward which can cause the door andtherefore the latch mounted on the door of the prior art designs to moveaway from engagement with the latching receptacle generally located onthe trim until the door latch becomes disengaged from the latchingreceptacle allowing the door to be pushed open by the overpressurecondition. In accordance with an aspect of the present invention, a newand improved latch is provided which, during an overpressure conditionwithin the load center, causes the latch to engage the latchingreceptacle on the trim even more securely so that the door does notdisengage and open.

Referring to FIG. 5, door 80 is shown mounted to trim panel 50 by hinges82. Mounted on face 84 of door 80 is door latch 120 shown in FIG. 6A.Door latch 120 is a one-piece molded member comprising a top 122 havingan indent 124 for engagement of the operator's finger for opening andclosing latch 120. Opening latch 120 is accomplished by sliding doorlatch 120 along the face 84 of door 80. As shown in FIG. 6B, extendingfrom the underside 126 of top 122 is a body portion 128 having aflexible tongue (or spring-like biasing member) 132 which extends in anupwardly direction from a lower portion of a sidewall 130 of bodyportion 128. Separately extending from the underside 126 of top 122 is agenerally "L" shaped fixed hook (or jaw) 134. The free end 136 of hook134 extends laterally in the direction of tongue 132.

Door 80 has a first cut out or opening 86 (shown in FIG. 5) sized topermit body portion 128 of latch 120 to pass through door 80. As shownin detail in FIG. 6E, there is a lip 90 in door 80 formed by bending themetal cut by lances for lip 90. Tongue 132 rests on lip 90 of door 80.The underside 126 of top 122 is positioned on the surface of door face84. Latch stop 138, shown in FIG. 6D, which extends from the underside126 of latch 120 is positioned against dimple 92 of first cutout 86, asshown in FIG. 5. A second cutout 88 in door 80 is sized to permit "U"shaped fixed hook 134 to pass through door 80.

Body portion 128 of door latch 120 is adapted to form a track 144 oneach of two sidewalls 140 to permit latch 120 to slide along the surfaceof door face 84 guided by edges 94 (shown in FIG. 5) of first cutout 86from an engaged position shown by FIG. 6E to a disengaged position.

Extending from each of sidewalls 140 of body 128 are inverted "C" shapedprojections. Tracks 144 are formed between the underside 126 of top 122and the upper edge 146 of inverted "C" shaped projections 142. Theinverted "C" shaped projections 142 fit into notches 96 shown in FIG. 5in first cutout 86. After installation of door latch 120 in door 80,inverted "C"-shaped projections 142 are not aligned with notches 96which thereby prohibit the removal of the door latch 120 from door 80.

Referring to FIG. 6E, door 80 is shown secured in a closed and latchedposition by door latch 120 with "L" shaped hook 134 which passes throughsecond cutout 88 in door 80 and through aperture 54 in trim panel 52(FIG. 3) to engage an underside edge 55 of aperture 54. In order todisengage latch 120 from its at rest closed position to enable theopening of door 80, the operator places one's finger in indent 124 oftop 122 and slides the latch toward the "free" end of door 80 (i.e., ina direction away from the door hinges). As latch 120 is slid along face84 toward the free end of door 80, flexible tongue (or basing member)132 is compressed against lip 90 thereby causing that "L" shaped hook134, which extends from the underside 126 of latch 120 and which isfaced inward towards hinges 82, to move out of engagement with underside55 of door 80 formed around aperture 54 and into vertical alignment withaperture 54 so that "L"-shaped hook 134 can pass freely through aperture54 thereby enabling the opening of door 80.

Latch 120 is maintained in a latched position by flexible tongue 132pressing against lip 90. The pressure of flexible tongue 132 against lip90, which keeps latch 120 in a closed position, is maintained by stop138 extending from the underside 126 of latch 120. Thus, latch 120 is ina biased closed position and, since "L" shaped fixed hook 134 is facedinward toward hinges 82 of the door 80, latch 120 remains in a biasedclosed position even if door 80 bows outwardly during an overpressurecondition within the load center 1.

Disposed within enclosure 10 is a basepan 200 to which is mounted thevarious components of the load center. Basepan 200 is made out of anelectrically insulative material which can be injection molded orextruded. One example of such material is a thermoplastic material soldunder the trademark Noryl by General Electric Company. Since loadcenters are constructed by a manufacturer in various sizes, a separateinventory of basepans had to be manufactured and maintained for eachsize load center. To decrease the expense and the need to maintainvarying sizes of basepans, an extruded basepan of the type described inU.S. Pat. Nos. 4,449,296 entitled "Method of Forming ElectricDistribution Panel", U.S. Pat. No. 4,536,823 entitled "Electric PanelBoard Having An Improved Extruded Basepan Configuration", U.S. Pat. No.4,740,865 entitled "Extruded Three-Phase Basepan Configuration For aLoad Center", and U.S. Pat. No. 5,081,560 entitled "Load CenterEnclosure" were introduced. Also, one or more individual modularauxiliary basepan pieces have been constructed for interconnection toform circuit breaker load centers of adjustable length. Such modularbasepan pieces are shown in U.S. Pat. Nos. 4,646,198, 5,450,282 and4,251,851. Because of difficulties involved in robotic assembly of thecomponents of the load center which require angular mounting,particularly molded basepans and modular extensions to provide basepansof varying length, and because of difficulties in assembling or securingcomponents to the basepan, modular extensions have been designed andmanufactured in the prior art to avoid the need for angular mounting.That is, modular extensions have been adapted to be vertically downloaded to mating portions of the basepan or have been adapted to behorizontally or laterally connected to mating portions of the basepan.

Such prior art attachment methods and modular constructions suffer frompossible misalignment and improper spacing between the connected pieces,which can affect the subsequent assembly and installation of componentsto the basepan. It would therefore be an advantage over the prior art tohave modular extension basepan components which need not be assembled insolely either a vertical drop-down mode or a lateral connected mode,which reduce the possibility of misalignment and improper spacingbetween connected modular pieces, and which can nevertheless berobotically assembled.

Referring to FIGS. 7 and 8, there is provided a snap-on basepan 200having a surface 202 upon which bus bars 400 and 440 are to be mounted,and circuit breaker support rails 204 from which extend circuit breakersupport hooks 206 for mounting and supporting circuit breakers. Each ofthe circuit breaker support rails 204 has an upper end wall 208, and alower end wall 210. In accordance with an aspect of the presentinvention, an improved basepan 200 is provided having a modularextension mounting foot 212 which extends from lower end wall 210 andupon which a modular extension basepan 300 (shown in FIG. 12) can bemounted in order to extend the length of snap-on basepan 200, andthereby enable a greater number of circuit breakers to be installedwithin the load center 1. Modular extension basepan 300 is also made outof an electrically insulative material which can be injection molded orextruded such as Noryl.

Referring to FIGS. 9 and 10, modular extension mounting foot 212 is inthe shape of a hollow rectangular box having an upper wall 214, twosidewalls 216 and 218, front wall 220, and a rear wall formed by lowerend wall 210 of circuit breaker support rail 204. Extending betweenmodular extension mounting feet 212 and from the lower edge of surface202 is a depressed platform 240 for mounting of a matching recessed edge332 of upper surface 302 of modular extension basepan 300. A trapezoidalshaped alignment slot 222, formed in upper wall 214 and sidewall 218 offoot 212 (shown in FIG. 9 and best seen in FIG. 11) is provided to beengaged by a correspondingly shaped alignment ramp 304 of modularextension basepan 300 (shown in FIG. 13 and best seen in FIG. 14) andthereby pulls modular extension basepan 300 toward and aligns withsnap-on basepan 200 when modular extension basepan 300 is mounted tosnap-on basepan 200. This properly positions modular extension basepan300 to snap-on basepan 200 for securing them together as more fullydescribed below. In order to secure modular extension basepan 300 tosnap-on basepan 200, upper wall 214 of mounting foot 212 has an aperture224 to allow a flexible snap hook 306 (FIGS. 13 and 14) of modularextension basepan 300 to pass and engage an upper edge 211A of slot 211formed in end wall 210 (FIG. 10) of circuit breaker support rail 204when modular extension basepan 300 is mounted to snap-on basepan 200.

Modular extension basepan 300 is configured to be substantially similarto snap-on basepan 200 in providing, for example, an upper surface 302,circuit breakers support rails 308, circuit breaker support hooks 310,double-walled serpentined bus bar barrier 334, integrally formed solidposts 342 and integrally formed hollow posts 344, and mounting tabs 336(for mounting snap-on basepan 200 and modular extension basepan 300 tothe metal enclosure 10 (FIG. 12).

Modular extension basepan 300 includes circuit breaker support rails 308having a cross-sectional shape of an inverted "U" (FIGS. 13 and 14). Onan inside wall 312 of circuit breaker support rail 308 at the proximateend of modular extension basepan 300 which is to be attached to thelower end of basepan 200, is trapezoidal shaped alignment ramp 304(FIGS. 13 and 14) which is complimentary in shape and size totrapezoidal shaped alignment slot 222 and positioned so that as modularextension basepan 300 is mounted to snap-on basepan 200, trapezoidalshaped ramp 304 is guided by trapezoidal slot 222 initially in adownward or Z-plan direction (shown by the "Z" arrows in FIG. 7), andthen laterally or horizontally in an X direction (shown by the "X"arrows in FIG. 7). This causes the modular extension basepan 300 to bebrought into abutting alignment with snap-on basepan 200. At the sametime, flexible snap hook 306 (FIGS. 13 and 14) passes through hole 224(FIG. 9) and engages edge 211A of slot 211 (FIGS. 10 and 11) in lowerend wall 210 of circuit breaker support rail 204 thereby securingmodular extension basepan 300 to snap-on basepan 200.

The result of causing modular extension basepan 300 to move in both avertical Z-direction and virtually simultaneously in a horizontalX-direction during mounting of modular extension basepan 300 beforesecuring to snap-on basepan 200, is a closer and more accurate fitbetween the modular extension basepan 300 and the snap-on basepan 200which in turn enables the accurate mounting of load center components tothe assembled basepan.

The distal end of modular extension basepan 300, which end is furthestaway from the lower end of snap-on basepan 200, is configured to besubstantially identical to the lower end of snap-on basepan 200. Thisconfiguration enables the successive attachment of modular extensionbasepans 300 to one another. Thus, referring to FIG. 12, modularextension basepan 300 has at its distal end two modular extensionmounting feet 314 each in the shape of a hollow rectangular box havingan upper wall 316, two sidewalls 318 and 320, front wall 322, and a rearwall formed by end face 309 of circuit breaker support rail 308. Atrapezoidal shaped alignment slot 324 is formed in upper wall 316 andside wall 320 in mounting feet 314 (FIGS. 15 and 16). Upper wall 316 hasan aperture 326 and end wall 309 of circuit breaker support rail 308 hasa slot 328 having an upper edge 328A (as does modular extension mountingfoot 212 of basepan 200). Extending between modular extension mountingfeet 314 is a depressed platform 330.

These elements and features of the snap-on basepan and modular extensionbasepan facilitate the robotic mounting of one to the other whileproviding for an accurate fit to one another.

In accordance with another aspect of the present invention, the portionof the enclosure to which a basepan is to be secured, and thecorresponding portion of the basepan which is used to secure the basepanto the enclosure, are improved so as to decrease the costs of theirmanufacturing and facilitate the assembly of the basepan to theenclosure.

Referring to FIGS. 7 and 8, basepan 200 is shown having ears 226disposed on opposite sides and each ear has an aperture 228 for mountingby a screw to a correspondingly positioned hole 32 in enclosure 10.Snap-on basepan 200 is also provided with tabs 230 extending laterallyfrom outer wall 209 of each circuit breaker support rail 204 (FIGS. 8and 18). Each tab 230 has a tapered lower edge 232 for capture between alance 34 formed in the backwall 12 of enclosure 10 and the interior faceof backwall 12. Tab 230 has a prong 234 extending laterally from a sideedge which is stopped by upper edge 36 of lance 34 thereby stopping thevertical movement of basepan 200 as it is installed in enclosure 10(FIG. 2). Lances 34 are stamped or cut from the backwall 12 of enclosure10 and bent into the interior of enclosure 10 as shown in FIG. 19. Thefree ends of lances 34 face one another, and capture tapered lower edge232 of tab 230 when basepan 200 is being installed within enclosure 10.Prongs 234 which extend from the side of each tab 230 are engaged by theupper edge 36 of lances 34 to stop the vertical movement of basepan 200during installation of the basepan to enclosure 10 while ears 226 ofbasepan 200 are placed into abutting relation with the interior surfaceof backwall 12 of enclosure 10.

Modular extension basepan 300 is also provided with tabs 336 extendinglaterally from outer wall 311 of each circuit breaker support rail 308(FIG. 12) and are otherwise structurally and functionally the same astabs 230 of snap-on basepan 200. Each tab 336 has a tapered lower edge338 and a prong 340 extending laterally from side edge 311 for capturebetween a lance 34 and the interior face of backwall 12. When modularextension basepan 300 has been mounted and secured to snap-on basepan200, tabs 336 and tabs 230 are captured by lances 34. The assembledmodular extension basepan 300 and snap-on basepan 200 is installedwithin and secured to enclosure 10 in the same way as basepan 200 aloneis installed in enclosure 10. The free end of lance 34 captures taperedlower edge 338 and upper edge 36 stops the vertical movement of basepan200 by capturing prong 340. Apertures 228 in ears 226 are brought intoalignment with correspondingly positioned holes 32 in backwall 12 andreceive a screw which retains the top end of basepan 200 to enclosure10.

Bus bars 400 and 440, which function to interconnect the line supplywith the distribution circuit breakers, have planar bus bars 402 and 442with integrally formed stabs or contact blades 404 and 444,respectively. Stabs 404 and 444 extend in parallel planes perpendicularto the longitudinal axis of each bus bar and are aligned in a row in ainterleaved face-to-face relation as shown in FIG. 20. Distributioncircuit breakers are electrically connected to the free end 406 and 446of stabs 404 and 444, respectively, and are supported in basepan 200 atone end by circuit breaker support rail 204 and at their other ends bybarrier 250. The free ends 404 and 446 of each of stabs 404 and 444 aremechanically and electrically connected within recesses in thedistribution circuit breakers and precludes a line to line short fromoccurring between a stab of bus bar 400 to a stab of bus bar 440. Sincethe positioning of the distribution circuit breakers on the stabs of thebus bars cannot preclude the possibility of a line to line short fromoccurring between one bus bar to the other bus bar, it is known in theart to provide an electrically insulative barrier between the bus barswhich increases the distance of the short circuit path, therebydecreasing the possibility that a short will occur.

In accordance with an aspect of the present invention, a double-walledserpentined electrical insulative barrier 250 between bus bars 400 and440 is provided which increases the protection from the occurrence of ashort, as well as decreasing the possibility of sustaining the short,once it has occurred. Referring to FIGS. 20 and 21, double-walledserpentined electrical insulative barrier 250 is shown comprising walls252 and 254 integrally formed with and extending substantiallyorthogonally upwards from planar surface 202 of basepan 200 and arepositioned on basepan 200 to provide a continuous double-walled physicalbarrier between bus bars 400 and 440.

Double-walled serpentined electrical insulative barrier 250 doubles thedistance that an arc must travel between planar busses 402 and 442 whichdecreases the possibility that arc tracking might occur as compared tothe prior art devices. Furthermore, doubling the distance that an arcmust travel also decreases the possibility of arc tracking, once it hasoccurred, from being able to reoccur. The circuitous path that the arcmust travel over and around walls 252 and 254 of barrier 250 as depictedby the dashed line in FIG. 22 also decreases the possibility that an arcwill track due to the length of the potential arc tracking path.

Bus bars have been secured to the basepan by common fastening devicessuch as screws, bolts and snap-in fasteners (U.S. Pat. No. 4,536,823)which can be cumbersome, time consuming, uneconomical, require extraparts and most importantly, can impart stresses to the component beingsecured and adversely effect the structural integrity of the basepan.

Applying ultrasonic energy to posts which are integral parts of aplastic basepan as a means of deforming the post to secure bus bars tothe plastic basepan is well known (U.S. Pat. No. 4,118,754). Heatstaking as a means of securing components to a plastic basepan can beadvantageous in overcoming the above-stated disadvantages of commonfastening devices, but imparts stresses which concentrate at the face ofthe basepan where the base of the post intersects the basepan to formcorners. Such stress can significantly impair the integrity of theconnection leading to a fracture of the post, loss of the integrity ofthe connection, and a decrease in the service life of the basepan andthe load center.

According to an aspect of the invention, an improved basepan havingintegrally formed posts for securing thereto components such as bus barsand the like by heat staking is provided, which improvement avoidsimparting stresses to the posts. Referring to FIG. 8, basepan 200 isshown having integrally formed solid posts 242 and integrally formedhollow posts 244 for mounting of bus bars 400 and 440. Referring to FIG.23 (which is a sectional view of a hollow post and the basepan), hollowpost 244, which is integrally formed with surface 202 of basepan 200, isshown having a torroidal shaped undercut 246 extending around theperiphery of hollow post 244 at its intersection or juncture withsurface 202. Torroidal shaped undercut 246 eliminates sharp corners atthe intersection or juncture between hollow post 244 and surface 202thereby reducing the stress concentration which can render hollow post244 susceptible to fracture from surface 202 due to heat staking. Asshown in FIG. 24, solid post 242 similarly has a torroidal shapedundercut 246 extending around its periphery at its intersection withsurface 202. Torroidal shaped undercuts 346 are similarly provided withintegrally formed solid posts 342 and integrally formed hollow posts 344of modular extension basepan 300 (FIG. 12).

Referring to FIG. 20, split neutral bars 500 each of which constitute anelectrically conductive common junction for the connection of returnwires of distribution circuits to the main power line return are shownmounted in channels 260 of basepan 200. In accordance with an aspect ofthe present invention, in order to improve the visibility of theelectrical connector apertures of the neutral bar into which the returnwires of the distribution circuits are to be inserted and secured, andthereby facilitate the connection of the return wires to the neutralbars by the electrical installer, each neutral bar has a central portionhaving a generally trapezoidal shaped cross-sectional area withoutwardly sloping sidewalls. Such configuration permits viewing of theelectrical connector apertures positioned in the sidewalls from variouspositions such as either orthogonally or directly overhead, or from theside. Referring to FIG. 25 which is a cross-sectional view of neutralbar 500 shown in FIG. 20 taken along line 25--25, neutral bar 500 has acentral body portion 510 having a generally trapezoidal shapedcross-sectional area with outwardly sloping sidewalls 512 and 514.Electrical return wire connector apertures 516 are provided in thesidewalls 512 and 514 of neutral bar 500. Top portion 502 of neutral bar500 has a top wall 504 through which a series of tapped holes 506 areprovided each of which is in communication with correspondinglypositioned return wire connector aperture 516. Positioned within eachtapped hole 506 is a threaded clamping screw 508 to secure the returnwire to the neutral bar.

The positioning of apertures 516 in the side walls 512 and 514 of thegenerally trapezoidal shaped cross-sectional area body 510 of neutralbar 500 enables the field installer to readily visually correlate theparticular aperture into which a selected corresponding electricalreturn wire is to be inserted and subsequently secured by a clampingscrew 508. Thus, as shown in FIG. 26, when viewing neutral bar 500orthogonally (i.e. directly overhead) as shown for example, in the topview of neutral bar 500 with screws 508 removed, each of tapped holes506 in top wall 504 and each of correspondingly positioned electricalconnector apertures 516 in side walls 512 and 514 are readily observedand located thereby facilitating proper insertion and connection of thereturn wires to the neutral bar.

In accordance with an aspect of the present invention, neutral bar 500is also adapted to permit simplified assembly and mounting to basepan200 which does not require the use of screws or other separate fasteningdevices thereby reducing the number of components in the load center.Referring again to FIG. 25, extending from the central portion 510 ofneutral bar 500 is a base 520 adapted to have a "T"-shaped slot 530,formed by the space between two mounting rails 522 and 524, whichreceives securing means integrally formed with and extending upward fromchannels 260 of basepan 200. Referring to FIGS. 7, 8, and 20, thesecuring means of basepan 200 comprises upwardly extending alignmentblocks 262 which fit within the space between mounting rails 522 and 524to align neutral bar 500 within channel 260, and upwardly extendingflexible snap hooks 264 and 266 (FIG. 27) which snappingly engage ridges526 and 528, respectively, of mounting rails 522 and 524 (FIG. 25) tolockingly join neutral bar 500 to basepan 200. Neutral bar 500 canthereby be quickly and easily mounted to basepan 200 and is retained inplace without the need of any additional fastening devices. Althoughneutral bar 500 may be fabricated as a unitary cast or molded member, ina preferred embodiment, neutral bar 500 is manufactured from an extrudedmetal such as aluminum.

In order to further facilitate the installation of the return wires tothe neutral bars of the load center, in accordance with an aspect of thepresent invention, a neutral bar wire guide is provided which assiststhe electrician or installer in guiding the return wires of distributioncircuits into the electrical connector apertures in the neutral bars. Asshown in FIGS. 7, 8, and 20, integrally formed with basepan 200 are twoneutral bar wire guides 270 each of which comprises a wall 272 upwardlyextending from the surface of the basepan 200 at the edge of the channel260 and having semicircular slots 276 extending through wall 272 at topsurface 275 between an outerface 273 and innerface 274 where eachsemicircular slot 276 is separated from one another by teeth 277. Thestructure appears as a scalloped edge (FIG. 28). Each semicircular slot276 is positioned to receive a neutral return wire and guide the end ofthe wire through the slot 276 from the outerface 273 past the innerface274 and into a preselected electrical connector aperture 516 in neutralbar 500 (FIG. 20). Neutral bar 500 is positioned in channel 260 ofbasepan 200 so that each one of the electrical connector apertures 516which are to receive a neutral return wire are aligned with acorresponding one of the semicircular slots 276 in neutral bar wireguide 270 as shown in FIG. 20.

The alignment of the semicircular slots 276 in neutral bar wire guide270 with the electrical connector apertures 516 in neutral bar 500 alsoassists the electrical installer in locating the electrical connectorapertures 516 and reduces the time required to connect the neutralreturn wires. Teeth 277 of neutral bar wire guide 270 function to assistin maintaining electrical isolation between each neutral wire andground.

The use of neutral bar 500 having a trapezoidal shaped cross-sectionalarea with readily viewable electrical connection apertures 516 combinedwith the neutral bar wire guide 270 having semicircular slots 276 whichare aligned with the electrical connection apertures 516 of neutral bar500, particularly facilitates the connection of the neutral return wiresto the neutral bar by the electric installer.

In accordance with an aspect of the present invention, an improvedneutral tie bar 550 which mechanically and electrically connects neutralbars 500 together is provided. Referring to FIGS. 20 and 30 (which is atop view of neutral tie bar 550 shown in FIG. 20 with other componentsremoved for clarity of illustration), neutral tie bar 550 is anelectrically conducting member to electrically connect the neutral bars500 and has a center portion 552 and vertically offset laterallyextending ends 564 and 566 which are connected by screws 570 throughapertures 568 and into corresponding tapped apertures 506 in each ofneutral bars 500. Referring to FIG. 29 (which is a sectional view takenalong line 29--29 in FIG. 30), neutral tie bar 550 is shown comprising afirst elevated member 554 disposed between center portion 552 and eachend 564 and 566 which are adapted to form a cable lug 556 for receiving,in a horizontally disposed bore 558, a branch neutral cable which is tobe secured therein by threaded clamping screw 562 within verticallyextending tapped bore 560. Extending between first elevated member 554and end portion 566 is a second elevated member 572 which is adapted tohave a neutral cable lug 574 for receiving in a horizontally disposedbore 576 the incoming neutral cable which is to be secured therein bythreaded clamping screw 580 within tapped bore 578. Neutral tie bar 550is secured to basepan 200 by heat staking hollow post 238 which extendsupward from basepan 200 through aperture 582 (FIGS. 7 and 8).

In some applications in which the neutral bar of the load center is notor has not been connected to an external grounding bar and therefore hasnot been electrically grounded, there is nonetheless a need to assurethat there is no potential difference between the neutral and theground. In accordance with an aspect of the present invention, in orderto eliminate any potential difference between the neutral and ground ofthe load center, neutral tie bar 550 is adapted to be capable of beingelectrically connected to the outer metal enclosure 10 of the loadcenter. Since each power company providing service maintains thepotential of the neutral at or close to zero volts, the function ofconnecting the neutral of the load center to the ground is accomplishedby electrically connecting the neutral tie bar to the metal outerenclosure. Referring to FIG. 29, neutral tie bar 550 is adapted to havean aperture 586 for accepting a fastener (not shown) which passesthrough a correspondingly positioned hole in hollow post 248 in basepan200 (FIG. 8) and into a correspondingly positioned hole 38 in enclosure10 (shown in FIG. 2). Although neutral tie bar 550 may be fabricated asa unitary or molded member or by casting metal, in a preferredembodiment neutral tie bar 550 is manufactured from extruded aluminum.

A removable barrier is typically provided between the incoming servicemain lugs, which connect the incoming service or main lines to the loadcenter, and the remainder of the components in the load center. Inaccordance with an aspect of the present invention, a new and improvedmain lug insulator 600 is provided to separate the main line lugs fromthe remainder of the components in the load center. The improved mainlug insulator functions to: (a) insulate each of the main lugs from theneutral tie bar and neutral lugs; (b) reduce incidental shorting orinadvertent energization of current carrying conductors both duringfield installation as well as subsequent operation; and (c) maintainrequired over-surface and through-air spacing for cooling and expansionof the main lugs.

Main lug insulator 600 is an integrally formed member made of anelectrically insulative material which can be injection molded orextruded. Referring to FIG. 31 which is an isolated perspective view ofthe main lug insulator shown in FIG. 20, main lug insulator 600 has twotrough-shaped compartments 610A and 610B for the receipt of main lugs420 and 460, respectively. Each compartment 610A and 610B is comprisedof a platform 612 from which extends two upstanding partition walls 614and 616 having oppositely facing open ends 618 and 620. Open ends 620provides access for the receipt of bus bar connector 408 and 448 andopen ends 618 provide access for the receipt of the ends of power cables(FIG. 31B). Platform 612 of each compartment has a groove 638 extendingtransversely for the receipt of a rail on the underside of the main lugs420 and 460 to facilitate the positioning of each lug within eachcompartment.

Extending downward from the edge of each open end 618 and downward fromthe edge of each open end 620 are substantially parallel support legs622 and 624, respectively, which connect the two compartments togetherlaterally and which elevate each compartment vertically (FIGS. 31A, 31Cand 31E). Legs 622 and 624 are spaced apart so as to straddle the widthof the neutral tie bar 550 and suspend compartments 610A and 610Btransversely over the neutral tie bar when installed in the basepan 200.Leg 622 has a mounting bracket 628 which extends transversely therefromand is heat staked to secure main lug insulator 600 to post 280 inbasepan 200. Leg 624 has a face 625 which extends laterally between thetwo compartments 610A and 610B.

Extending from the underside of platform 612 of each compartment arebars 636 which are positioned so that when main lug insulator 600 isinstalled in the load center, bars 636 engage correspondingly positionedand shaped slots 584 in neutral tie bar 550. This functions to maintainthe position and alignment of the neutral tie bar together with the mainlug insulator for mounting by heat staking. Also extending from theunderside of platform 612 and outer face 630 of upstanding walls 616 ofeach of the compartments is an alignment member 632 which forms a slot634 with leg 624. When main lug insulator 600 is installed withinbasepan 200, slot 634 engages edges 284, 286, and 288 of upstandingbarrier member 282 of basepan 200 (FIG. 7) which completes the barrierbetween (a) the main lugs and bus bar connectors and (b) the neutrallugs and neutral tie bar as shown in FIG. 20.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

I claim:
 1. An electric load center comprising:a basepan having a planarsurface for mounting of components to the load center, the planarsurface having a tab extending from an edge of the planar surface, thetab having a tapered lower edge and a prong extending from a side edge,the basepan further having ears extending from the planar surface anddisposed toward opposite sides of the basepan, each of the ears havingan aperture for the passage of a screw; an enclosure having a lanceformed from a backwall of the enclosure, the lance having a free enddisposed away from the backwall and into the interior of the enclosurefor capturing the tab of the basepan, the enclosure further having ahole in the backwall for receiving a screw; so that as the basepan isbeing mounted to the enclosure, the tapered lower edge of the tab iscaptured between the lance formed in the backwall of the enclosure andthe interior face of the backwall and the prong is engaged by an upperedge of the lance to stop the vertical movement of the basepan while theears of the basepan are placed into abutting relation with the interiorsurface of the backwall for mounting by a screw through the aperture andinto the correspondingly positioned hole in the enclosure.
 2. A loadcenter comprising an enclosure having a backwall, a basepan mounted inthe enclosure and having a surface, bus bars mounted on the surface, atleast one circuit breaker support rail disposed on the surface formounting and supporting circuit breakers thereon, the basepan havingears disposed on the opposite sides thereof, each ear having an aperturefor accepting a fastener for mounting the basepan to the enclosure, theenclosure having a corresponding hole, the basepan further having tabswhich extend laterally from an outerwall of the circuit breaker supportrail, each of the tabs having a tapered lowered edge for capture betweenat least one lance extending from the back wall of the enclosure and aninterior face of the back wall, each of the tabs having a prong extendedlaterally from a side edge thereof which engages an upper edge of the atlease one lance to stop vertical movement of the basepan when installedin the enclosure.
 3. The load center of claim 2 wherein the at least onelance is cut from the backwall of the enclosure and bent into aninterior of the enclosure.
 4. The basepan of claim 2 wherein the atleast one lance is a plurality of lances arranged in pairs of lancesdisposed in a facing position for capturing the tapered lower edges ofeach of the tabs when the basepan is installed within the enclosure. 5.The basepan of claim 2 further comprising prongs which extend from thesides of each tab for engagement by upper edges of the at least onelance.
 6. The basepan of claim 2 further comprising a modular extensionbasepan mounted to the basepan, the modular extension basepan havingtabs which extend laterally from an outer wall of at least one circuitbreaker support rail mounted on the modular extension basepan, each tabhaving a tapered lowered edge and a prong extended laterally from a sideedge thereof for capture between at least one lance extending from theback wall of the enclosure and an interior face of the back wall, tostop vertical movement of the modular extension basepan when installedin the enclosure.